I use Crayola Bathtub Markers. I also have Aquanotes Pad and Pen when I want to soak in Green Tea in the tub.
In the car while driving I have my handheld digital recorder.
I love it, thank you for the water-safe ideas!
I tried video-recording myself while driving as I have to sign not talk and I don't like watching myself, doesn't quite flow for me.